Single Chain FC Polypeptides

ABSTRACT

The present invention relates to single chain polypeptides comprising one or more immunoglobulin Fc domains. In particular the present invention relates to single-chain Fc polypeptides in which at least one functional Fc domain is formed within the polypeptide chain.

The present invention relates to single chain polypeptides comprising one or more immunoglobulin Fc domains. In particular the present invention relates to single-chain polypeptides in which at least one functional Fc domain is formed within the chain.

Immunoglobulins are bivalent Y-shaped molecules comprising two identical heavy chains and two identical light chains. Disulfide bonds link together the heavy and light chain pairs as well as the two heavy chains. Each chain consists of one variable domain that varies in sequence and is responsible for antigen binding, these are known as the V_(H) and V_(L) domains for the heavy and light chains respectively. Each chain also consists of at least one constant domain. In the light chain there is a single constant domain (C_(L)) and in the heavy chain there are at least three (C_(H)1, C_(H)2 and C_(H)3), sometimes four (C_(H)4) depending on the isotype. In humans there are five different classes or isotypes of antibodies including IgA (which includes IgA1 and IgA2), IgD, IgE, IgG (which includes subclasses IgG1, IgG2, IgG3 and IgG4) and IgM.

The Fc domain of an antibody typically comprises at least the last two heavy chain constant region domains of each chain which dimerise to form the Fc domain. The Fc domain is responsible for providing antibody effector functions, including determining antibody half-life and distribution throughout the body, ability to fix complement and binding to cell surface Fc receptors. The properties of Fc domains have made them useful therapeutic agents and Fc domains have been fused to other non-antibody proteins, such as receptor proteins e.g. etanercept. Fc domain fusions have also been used as research reagents, ‘Fc tags’, which facilitate fusion protein detection and purification. In addition, a number of alternative antibody structures comprising Fc domains have also been described see for example Dumont et al., 2006, Biodrugs, 20(3) 151-160, WO2005001025, WO2005077981, WO2005017148 and Hayden et al., 1994, Therapeutic Immunology, 1, 3-15. WO2005077981 describes antibodies in which each chain comprises two Fc domains i.e. each antibody chain comprises in linear sequence CH2 CH3 CH2 CH3 and these domains dimerise to form two functional Fc domains to provide enhanced effector functions. WO2005017148 and Hayden et al. supra describe single chain polypeptides comprising a single-chain Fv fused to half of an Fc domain i.e. sc-Fv-CH2 CH3. These polypeptides can exist as both monomers or dimers.

The binding specificity of antibodies has made these useful therapeutic agents, however, bivalent molecules such as antibodies are often inappropriate targeting agents for certain cell surface antigens. Bivalent binding can cause the target cell to undergo co-stimulation, activation and/or antigenic modulation, thereby offering the cell a means of evading complement and the various effector cells recruited by the Fc domain of the antibody. Instead, in order to target such cell surface antigens antibodies have typically been conjugated to drugs or toxins that kill the cells upon internalization.

In contrast, univalent antibody fragments do not cause antigenic modulation as no redistribution of surface antigen occurs and hence no co-stimulation and no internalization. It would be desirable therefore to retain the natural effector functions of an antibody in such fragments and thus avoid the need for costly and time consuming attachment of drugs or toxins. An example of one such antibody fragment was produced by proteolytic cleavage of a rabbit IgG by Glennie and Stevenson, 1982, Nature, 295, 712-713. The fragment comprised only a single Fab binding site but retained the entire Fc domain. The fragment was produced by papain digestion of a rabbit IgG antibody A12 allotypic variant which is glycosylated on one chain, making that chain resistant to papain digestion, thus allowing one Fab arm to be retained. The fragment produced was demonstrated to be more effective in invoking complement mediated lysis of cells than the whole IgG. Similar fragments have been produced from human IgG by proteolytic digestion (Michaelsen and Natvig, Scand. J. Immunology, 1973, 2, 299-312; Michaelsen and Natvig, Scand. J. Immunology, 1972, 1, 255-268) and by chemical cleavage (Wines and Easterbrook-Smith, Molecular Immunology, 1991, 28, 8, 855-863). These fragments are not practical to produce on a commercial scale as the use of proteolysis requires long preparation times and results in low yields and mixed products.

WO20050010125 describes hybrid proteins comprising two polypeptide chains, the first polypeptide chain comprising an Fc region and a biologically active molecule and the second polypeptide chain comprising an Fc region without the biologically active molecule of the first chain. The two chains are produced separately and are either allowed to dimerise or are chemically conjugated together. Although this achieves the desired functional molecule, the preparation is complex and involves low yielding chromatographic procedures.

Surprisingly we have now found that it possible to produce a functional Fc domain as a single-chain polypeptide. The polypeptides of the present invention therefore have the advantage that they can be produced recombinantly in large amounts and can be linked by any suitable means to any other molecule, such as a binding domain. Further, as the antibody constant domains form an Fc domain within the chain, the polypeptides of the present invention are not prone to dimerization thus, where desired, bi-valent binding domains can be avoided.

Accordingly the present invention provides a single chain polypeptide comprising two CH2 domains and two CH3 domains characterized in that said CH2 and CH3 domains form a functional Fc domain within the chain. The functional Fc domain in the single-chain polypeptides of the present invention is not formed by dimerization of two chains i.e. the two CH2 domains and two CH3 domains are present in a single chain and form a functional Fc domain within the single chain. Accordingly the present invention provides a single chain polypeptide comprising two CH2 domains and two CH3 domains characterized in that said CH2 and CH3 domains form a functional Fc domain within the chain and not by dimerization with another polypeptide chain. Accordingly, in the single chain polypeptide of the present invention a first CH2 domain is dimerized with a second CH2 domain and a first CH3 domain is dimerized with a second CH3 domain within the polypeptide chain.

The term ‘functional’ as used herein refers to the ability of the Fc domain formed within the single chain polypeptide to provide one or more effector functions usually associated with Fc domains although it will be appreciated that other functions may be engineered into such domains. Examples of effector functions include determining the half-life and/or distribution of the Fc polypeptide throughout the body, the ability of the Fc polypeptide to fix complement and the ability of the Fc polypeptide to bind to cell surface Fc receptors. Examples of such effector functions include but are not limited to, antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP) and complement-dependent cytotoxicity (CDC).

The Fc domain of the present invention comprises four or more constant domains which may be derived from any suitable species and/or class of antibody. Preferably the constant domains are human. In humans there are five different classes or isotypes of antibodies including IgA (which includes IgA1 and IgA2), IgD, IgE, IgG (which includes subclasses IgG1, IgG2, IgG3 and IgG4) and IgM. Any suitable Fc domain may be used depending on the effector functions required. Typically the term Fc domain as used herein refers to the last two constant region immunoglobulin domains of IgA, IgD and IgG (CH2 and CH3) and the last three constant region domains of IgE and IgM (CH2, CH3 and CH4), although it will be appreciated that in certain circumstances not all the domains may be required, for example in the case of IgE or IgM only CH2 and CH3 domains may be sufficient. It will also be appreciated that more than one Fc domain may be formed within the single chain Fc polypeptide and that these Fc domains may be derived from the same or different isotypes.

The residues in antibody domains are conventionally numbered according to a system devised by Kabat et al. This system is set forth in Kabat et al., 1987, in Sequences of Proteins of Immunological Interest, US Department of Health and Human Services, NIH, USA (hereafter “Kabat et al. (supra)”). This numbering system is used in the present specification except where otherwise indicated.

In one embodiment the Fc domain is derived from IgA and the single-chain Fc polypeptide comprises two Cα2 domains and two Cα3 domains.

In one embodiment the Fc domain is derived from IgM and the single-chain Fc polypeptide comprises two Cμ2 domains, two Cμ3 domains and two Cμ4 domains.

In one embodiment the Fc domain is derived from IgD and the single-chain Fc polypeptide comprises two Cδ2 domains and two Cδ3 domains.

In one embodiment the Fc domain is derived from IgE and the single-chain Fc polypeptide comprises two Cε2 domains, two Cε3 domains and two Cε4 domains.

Preferably the Fc domain of the present invention is derived from an IgG and the single-chain Fc polypeptide comprises two Cγ2 and two Cγ3 domains. The preferred sequences for the Cγ2 domain of IgG1, IgG2, IgG3 and IgG4 for use in the present invention are provided in SEQ ID NOS: 2, 15, 28 and 41 respectively and the preferred sequences for the Cγ3 domain of IgG1, IgG2, IgG3 and IgG4 for use in the invention are provided in SEQ ID NOS: 3, 16, 29 and 42 respectively.

Accordingly, in one embodiment the present invention provides a single chain polypeptide comprising two Cγ2 domains and two Cγ3 domains characterized in that said Cγ2 and Cγ3 domains form a functional Fc domain within the chain i.e. a first Cγ2 domain dimerizes with a second Cγ2 domain and a first Cγ3 domain dimerizes with a second Cγ3 domain within the polypeptide chain

It will be appreciated that the constant region domains for use in producing the Fc domain of the present invention may include variants of the naturally occurring constant domains described herein above. Such variants may comprise one or more amino acid variations compared to wild type constant domains. In one example the Fc domain of the present invention comprises at least one constant domain which varies in sequence from the wild type constant domain. It will be appreciated that the variant constant domains may be longer or shorter than the wild type constant domain. Preferably the variant constant domains are at least 50% identical or similar to a wild type constant domain. The term “Identity”, as used herein, indicates that at any particular position in the aligned sequences, the amino acid residue is identical between the sequences. The term “Similarity”, as used herein, indicates that, at any particular position in the aligned sequences, the amino acid residue is of a similar type between the sequences. For example, leucine may be substituted for isoleucine or valine. Other amino acids which can often be substituted for one another include but are not limited to:

-   -   phenylalanine, tyrosine and tryptophan (amino acids having         aromatic side chains);     -   lysine, arginine and histidine (amino acids having basic side         chains);     -   aspartate and glutamate (amino acids having acidic side chains);     -   asparagine and glutamine (amino acids having amide side chains);         and     -   cysteine and methionine (amino acids having sulphur-containing         side chains).         Degrees of identity and similarity can be readily calculated         (Computational Molecular Biology, Lesk, A. M., ed., Oxford         University Press, New York, 1988; Biocomputing. Informatics and         Genome Projects, Smith, D. W., ed., Academic Press, New York,         1993; Computer Analysis of Sequence Data, Part 1, Griffin, A.         M., and Griffin, H. G., eds., Humana Press, New Jersey, 1994;         Sequence Analysis in Molecular Biology, von Heinje, G., Academic         Press, 1987; and Sequence Analysis Primer, Gribskov, M. and         Devereux, J., eds., M Stockton Press, New York, 1991). In one         example the variant constant domains are at least 60% identical         or similar to a wild type constant domain. In another example         the variant constant domains are at least 70% identical or         similar. In another example the variant constant domains are at         least 80% identical or similar. In another example the variant         constant domains are at least 90% identical or similar. In         another example the variant constant domains are at least 95%         identical or similar.

In one embodiment the variant constant domains provide equivalent Fc effector functions compared to the wild type Fc domain. In one embodiment the variant constant domains provide improved effector functions. In one embodiment the variant constant domains provide altered effector functions. In one example the Fc domain provides no effector functions other than extended half-life. In one example the Fc domain provides FcR binding but not C1q binding. In one example the Fc domain provides C1q binding but not FcR binding.

A number of Fc variant polypeptides are known in the art, see for example Idusogie et al., Journal of Immunology, 2000, 164, 4178-4184 and Shields et al., Journal of Biological Chemistry, 2001, 276, 9, 6591-6604. A comprehensive list of Fc variants is provided by WO2005077981 (see in particular, paragraph number 80) and these are incorporated herein by reference.

Examples of Fc variants include in IgG1 N314Q (or N297Q), T318A (T299A), A349S (A330S) with P350A (P331A), L247A (L234A) with L248A (L235A) or P348A (P329A) (number in brackets is EU numbering). Where the IgG4 Fc domain is used the S241P (S228P) mutation may be used (Angal et al., Molecular Immunology, 1993, 30 (1), 105-108). It will be appreciated that any suitable variant may be produced and tested using routine methods known in the art.

The CH2, CH3 and where present CH4 domains of the single-chain Fc polypeptide of the present invention are linked in the single polypeptide chain such that they can still form a functional Fc domain within the chain. Accordingly any suitable amino acid linkers may be used to link these constant domains provided they allow a functional Fc domain to form within the single-chain polypeptide. Suitable amino acids for use in linkers of the present invention include, but are not limited to, small flexible amino acids such as Gly, Ser, Ala and Thr. In one embodiment the linker comprises or consists of glycine residues. In one embodiment the linker comprises or consists of serine residues. In one embodiment the linker comprises or consists of alanine residues. In one embodiment the linker comprises or consists of threonine residues. In one embodiment the linker comprises or consists of glycine and serine residues. In one embodiment the linker comprises or consists of glycine, serine and alanine residues. In one embodiment the linker comprises or consists of glycine, serine, alanine and threonine residues. For the avoidance of doubt, it is understood that all permutations of glycine and/or serine and/or alanine and/or threonine residues are included. In one example the linker comprises or consists of 30-80% glycine residues and 20-70% serine residues. In one example the linker comprises or consists of 35-50% glycine residues; 30-40% serine residues; 5-15% threonine residues and 10-20% alanine residues. In one example the amino acid residues are randomly distributed within the linker. Specific examples of suitable linkers include glycine-serine polymers comprising for example repeats of sequences such as GS, GSGGS, GGGGS and GGGS.

In one embodiment the Fc domain of the single chain polypeptide of the present invention comprises two CH2 domains and two CH3 domains.

In one embodiment the present invention provides a single chain Fc polypeptide comprising two CH2 domains and two CH3 domains wherein in N— to C-terminal sequence, a first CH2 domain is linked at its C-terminus to the N-terminus of a first CH3 domain and said first CH3 domain is linked at its C-terminus via a linker to the N-terminus of a second CH2 domain which is linked at its C-terminus to the N-terminus a second CH3 domain (as shown in FIG. 1).

In one embodiment the first CH2 domain is directly linked i.e. genetically fused at its C-terminus to the N-terminus of the first CH3 domain.

In one embodiment the second CH2 domain is directly linked i.e. genetically fused at its C-terminus to the N-terminus of the second CH3 domain.

Examples of suitable CH2 domains genetically fused to CH3 domain(s) are given in SEQ ID NOS: 5, 18, 31 and 44.

In one embodiment a linker is employed to link the C-terminus of the first CH2 domain to the N-terminus of the first CH3 domain.

In one embodiment a linker is employed to link the C-terminus of the second CH2 domain to the N-terminus of the second CH3 domain.

Where a linker is used to link (i) the C-terminus of the first CH2 domain to the N-terminus of the first CH3 domain and/or (ii) the C-terminus of the second CH2 domain to the N-terminus of the second CH3 domain the linker will be of sufficient length to allow a functional Fc domain to form within the chain. Typically the linker will only be a few amino acids in length, preferably less than 10 amino acids in length. Where a linker is used in both (i) and (ii) above the two linkers may be the same or different. Preferably the linkers will be approximately the same length.

The linker used to link the C-terminus of the first CH3 domain to the N-terminus of the second CH2 domain will be sufficiently long to allow a functional Fc domain to form within the chain i.e. it will be sufficiently long to allow a first CH2 domain to dimerise with a second CH2 domain and a first CH3 domain to dimerise with a second CH3 domain within the polypeptide chain. In one embodiment the linker is around 30-100 amino acids in length, in another embodiment the linker is around 40 to 100 amino acids in length. In one embodiment the linker is around 40 to 90 amino acids in length. In one embodiment the linker is around 40 to 80 amino acids in length, preferably 40 to 70 amino acids in length. Suitable amino acids for use in these linkers are described herein above. In one example the linker comprises or consists of 35-50% glycine residues; 30-40% serine residues; 5-15% threonine residues and 10-20% alanine residues. In one example the amino acid residues are randomly distributed within the linker. An example of a suitable linker is provided in SEQ ID NO:62. In one embodiment the linker may comprise, preferably towards its C-terminus one or more cysteine residues. In one embodiment the linker may comprise at its C-terminus the sequence of all or part of the hinge region of an antibody or variant thereof comprising one or more cysteine residues. Examples of suitable hinge sequences for use in the linkers of the present invention are provided in U.S. Pat. No. 5,677,425, WO9915549, WO9825971 and WO2005003171 and these are incorporated herein by reference. Other examples of suitable hinges are provided in SEQ ID NOs:53-57. Accordingly, in one example the linker of SEQ ID NO:62 further comprises at its C-terminus any one of the sequences provided in SEQ ID NOs: 53-57. In this embodiment, the linker is around 30 to 130 amino acids in length. In one embodiment the linker is around 50 to 100 amino acids in length. In one embodiment the linker is around 50 to 80 amino acids in length.

In another embodiment, the present invention provides a single chain Fc polypeptide comprising two CH2 domains and two CH3 domains wherein in N— to C-terminal sequence a first CH2 domain is linked at its C-terminus via a linker to the N-terminus of a second CH2 domain and said second CH2 domain is linked at its C-terminus to the N-terminus of a first CH3 domain and said first CH3 domain is linked at its C-terminus to the N-terminus of a second CH3 domain via a linker (as shown in FIG. 2).

In one embodiment the second CH2 domain is genetically fused at its C-terminus to the N-terminus of the first CH3 domain.

In one embodiment the C-terminus of the second CH2 domain is connected by a linker to the N-terminus of the first CH3 domain.

Where a linker is used to link the C-terminus of the second CH2 domain to the N-terminus of the first CH3 domain the linker will be of sufficient length to allow a functional Fc domain to form within the chain. Typically the linker will only be a few amino acids in length, preferably less than 10 amino acids in length.

The linker used to link the C-terminus of the first CH2 domain to the N-terminus of the second CH2 domain and the linker used to link the C-terminus of the first CH3 domain to the N-terminus of the second CH3 domain will be sufficiently long to allow a functional Fc domain to form within the chain. It will be appreciated that these two linkers may be the same or different in both composition and/or length. In one embodiment one or both of the linkers is between 15 and 50 amino acids in length. In one embodiment one or both of the linkers is between 15 and 40 amino acids in length. In one embodiment one or both of the linkers is between 20 and 40 amino acids in length. In another embodiment one or both of the linkers is between 20 and 35 amino acids in length. Suitable amino acids for use in these linkers are described herein above. In one example one or both of the linkers comprises or consists of 50-80% glycine residues and 10-30% serine residues. In one example the amino acid residues are randomly distributed within the linker. In one example the linker comprises the sequence (GGGGS)n where n=3 to 8. In one embodiment the linker between the C-terminus of the first CH2 domain and the N-terminus of the second CH2 domain comprises the sequence (GGGGS)n where n=5 (SEQ ID NO:63). In one embodiment the linker between the C-terminus of the first CH3 domain and the N-terminus of the second CH3 domain comprises the sequence (GGGGS)n where n=5 (SEQ ID NO:63).

In one embodiment the linker between the first CH2 domain and the second CH2 domain comprises, preferably towards its C-terminus, one or more cysteine residues. In one embodiment the linker comprises all or part of an antibody hinge sequence or variant thereof as described herein above. Accordingly, in one embodiment the linker between the C-terminus of the first CH2 domain and the N-terminus of the second CH2 domain having the sequence given in SEQ ID NO:63 further comprises at its C-terminus any one of the hinge sequences provided in SEQ ID NOs 53-57. In this embodiment the linker between the C-terminus of the first CH2 domain and the N-terminus of the second CH2 domain is between 25 and 90 amino acids in length. In one embodiment this linker is between 25 and 80 amino acids in length. In one embodiment this linker is between 25 and 70 amino acids in length. In one embodiment this linker is between 25 and 60 amino acids in length. In one embodiment this linker is between 25 and 50 amino acids in length. In one embodiment this linker is between 25 and 40 amino acids in length.

In one embodiment the Fc domain of the single chain Fc polypeptide of the present invention comprises two CH2 domains, two CH3 domains and one or two CH4 domains, preferably two.

In one embodiment the present invention provides a single chain Fc polypeptide comprising two CH2 domains, two CH3 domains and two CH4 domains wherein in N— to C-terminal sequence, a first CH2 domain is linked at its C-terminus to the N-terminus of a first CH3 domain, said first CH3 domain is linked at its C-terminus to the N-terminus of a first CH4 domain and said first CH4 domain is linked at its C-terminus via a linker to the N-terminus of a second CH2 domain which is linked at its C-terminus to the N-terminus of a second CH3 domain which is linked at its C-terminus to the N-terminus of a second CH4 domain (see for example FIG. 3 a).

In one embodiment one or more of the following domains are directly linked i.e. genetically fused (i) the C-terminus of the first CH2 domain to the N-terminus of the first CH3 domain (ii) the C-terminus of the second CH2 domain to the N-terminus of the second CH3 domain (iii) the C-terminus of the first CH3 domain to the N-terminus of the first CH4 domain (iv) the C-terminus of the second CH3 domain to the N-terminus of the second CH4 domain.

In one embodiment one or more of the following domains are connected by a linker (v) the C-terminus of the first CH2 domain to the N-terminus of the first CH3 domain (vi) the C-terminus of the second CH2 domain to the N-terminus of the second CH3 domain (vii) the C-terminus of the first CH3 domain to the N-terminus of the first CH4 domain (viii) the C-terminus of the second CH3 domain to the N-terminus of the second CH4 domain.

Where a linker is present between any one of (v, vi, vii or viii) this linker will be of sufficient length to allow a functional Fc domain to form within the chain. Typically the linker will only be a few amino acids in length. Where there is more than one linker it will be appreciated that these may be the same or different. Preferably the linkers will be approximately the same length.

The linker used to link the C-terminus of the first CH4 domain to the N-terminus of the second CH2 domain will be sufficiently long to allow a functional Fc domain to form within the chain. In one embodiment the linker is around 50-100 amino acids in length, in another embodiment the linker is around 60 to 100 amino acids in length. In one embodiment the linker is around 70 to 100 amino acids in length, preferably 80 to 100 amino acids in length. Suitable amino acids for use in these linkers have been described herein above. In one embodiment the linker may comprise, preferably towards its C-terminus, one or more cysteine residues. In one embodiment the linker comprises all or part of an antibody hinge sequence or variant thereof as described herein above.

In another embodiment, the present invention provides a single chain Fc polypeptide comprising two CH2 domains, two CH3 domains and two CH4 domains wherein in N— to C-terminal sequence a first CH2 domain is linked at its C-terminus via a linker to the N-terminus of a second CH2 domain and said second CH2 domain is linked at its C-terminus to the N-terminus of a first CH3 domain and said first CH3 domain is linked at its C-terminus to the N-terminus of a first CH4 domain which is linked at its C-terminus, via a linker, to the N-terminus of a second CH3 domain which is linked at its C-terminus to the N-terminus of a second CH4 domain (see for example FIG. 3 b).

In one embodiment one or more of the following domains are directly linked i.e. genetically fused (i) the C-terminus of the second CH2 domain to the N-terminus of the first CH3 domain (ii) the C-terminus of the first CH3 domain to the N-terminus of the first CH4 domain (iii) the C-terminus of the second CH3 domain to the N-terminus of the second CH4 domain.

In one embodiment one or more of the following domains are connected by a linker (i) the C-terminus of the second CH2 domain to the N-terminus of the first CH3 domain (ii) the C-terminus of the first CH3 domain to the N-terminus of the first CH4 domain (iii) the C-terminus of the second CH3 domain to the N-terminus of the second CH4 domain.

Where a linker is present between one or more of (i) the C-terminus of the second CH2 domain and the N-terminus of the first CH3 domain (ii) the C-terminus of the first CH3 domain and the N-terminus of the first CH4 domain (iii) the C-terminus of the second CH3 domain and the N-terminus of the second CH4 domain the linker will be of sufficient length to allow a functional Fc domain to form within the chain. Typically the linker will only be a few amino acids in length. Where there is more than one linker it will be appreciated that these may be the same or different. Preferably the linkers will be approximately the same length.

The linker between the C-terminus of the first CH2 domain and the N-terminus of the second CH2 domain and the linker between the C-terminus of the first CH4 domain and the N-terminus of the second CH3 domain will be sufficiently long to allow a functional Fc domain to form within the chain. Suitable amino acids for these linkers have been described herein above.

The linker between the C-terminus of the first CH2 domain and the N-terminus of the second CH2 domain is typically between 15 and 40 amino acids in length. In another embodiment the linker is between 20 and 35 amino acids in length. In one embodiment the linker between the C-terminus of the first CH2 domain and the N-terminus of the second CH2 domain comprises the sequence (GGGGS)n where n=5 (SEQ ID NO:63).

In one embodiment the linker between the first CH2 domain and the second CH2 domain comprises, preferably towards its C-terminus, one or more cysteine residues. In one embodiment the linker comprises all or part of an antibody hinge sequence or variant thereof as described herein above which may comprise one or more cysteine residues. Suitable hinge sequences include those provided in SEQ ID NOs 53-57.

The linker between the C-terminus of the first CH4 domain and the N-terminus of the second CH3 domain is typically around 30-100 amino acids in length, in another embodiment the linker is around 40 to 100 amino acids in length. In one embodiment the linker is around 40 to 80 amino acids in length, preferably 40 to 70 amino acids in length. An example of a suitable linker is provided in SEQ ID NO:62.

In another embodiment, the present invention provides a single chain Fc polypeptide comprising two CH2 domains, two CH3 domains and two CH4 domains wherein in N— to C-terminal sequence a first CH2 domain is linked at its C-terminus to the N-terminus of a first CH3 domain and said first CH3 domain is linked at its C-terminus via a linker to the N-terminus of a second CH2 domain and said second CH2 domain is linked at its C-terminus to the N-terminus of a second CH3 domain which is linked at its C-terminus to the N-terminus of a first CH4 domain which is linked at its C-terminus, via a linker, to the N-terminus of a second CH4 domain (see for example FIG. 1 c).

In one embodiment one or more of the following domains are directly linked i.e. genetically fused (i) the C-terminus of the first CH2 domain and the N-terminus of the first CH3 domain (ii) the C-terminus of the second CH2 domain and the N-terminus of the second CH3 domain (iii) the C-terminus of the second CH3 domain and the N-terminus of the first CH4 domain.

In one embodiment one or more of the following domains are connected by a linker (i) the C-terminus of the first CH2 domain and the N-terminus of the first CH3 domain (ii) the C-terminus of the second CH2 domain and the N-terminus of the second CH3 domain (iii) the C-terminus of the second CH3 domain and the N-terminus of the first CH4 domain.

Where a linker is present between one or more of (i) the C-terminus of the first CH2 domain and the N-terminus of the first CH3 domain (ii) the C-terminus of the second CH2 domain and the N-terminus of the second CH3 domain (iii) the C-terminus of the second CH3 domain and the N-terminus of the first CH4 domain the linker will be of sufficient length to allow a functional Fc domain to form within the chain. Typically the linker will only be a few amino acids in length. Where there is more than one linker it will be appreciated that these may be the same or different. Preferably the linkers will be approximately the same length.

The linker between the C-terminus of the first CH3 domain and the N-terminus of the second CH2 domain and the linker between the C-terminus of the first CH4 domain and the N-terminus of the second CH4 domain will be of sufficient length to allow a functional Fc domain to form within the chain.

The linker between the C-terminus of the first CH4 domain and the N-terminus of the second CH4 domain is typically between 15 and 40 amino acids in length. In another embodiment the linker is between 20 and 35 amino acids in length. In one embodiment the linker between the C-terminus of the first CH4 domain and the N-terminus of the second CH4 domain comprises the sequence (GGGGS)n where n=5 (SEQ ID NO:63).

The linker between the C-terminus of the first CH3 domain and the N-terminus of the second CH2 domain is typically around 30-100 amino acids in length, in another embodiment the linker is around 40 to 100 amino acids in length. In one embodiment the linker is around 40 to 80 amino acids in length, preferably 40 to 70 amino acids in length. An example of a suitable linker is provided in SEQ ID NO:62.

In one embodiment the linker between the first CH3 domain and the second CH2 domain comprises, preferably towards its C-terminus, one or more cysteine residues. In one embodiment this linker comprises all or part of an antibody hinge sequence or variant thereof as described herein above which may comprise one or more cysteine residues. Suitable hinge sequences include SEQ ID NOs 53-57.

In one embodiment the single chain Fc polypeptide of the present invention further comprises an amino acid linker genetically fused to the N-terminus of the first CH2 domain. The linker may comprise any suitable amino acids and be of any suitable length. In one embodiment the linker comprises one or more cysteine residues. In one embodiment the linker genetically fused to the N-terminus of the first CH2 domain comprises all or part of an antibody hinge sequence or variant thereof as described herein above. In one embodiment the linker comprises the sequence given in any one of SEQ ID NOs:53-57. In one embodiment one or more of the cysteine residues present in the linker are disulphide linked to one or more cysteine residues present in any one of the following linkers where present (i) the linker which connects the C-terminus of the first CH3 domain and the N-terminus of the second CH2 domain (see for example FIG. 1 a) (ii) the linker which connects the C-terminus of the first CH2 domain to the N-terminus of the second CH2 domain (see for example FIG. 2 a) or (iii) the linker which connects the C-terminus of the first CH4 domain to the N-terminus of the second CH2 domain.

In another embodiment the linker fused to the N-terminus may comprise all or part of the hinge region of an antibody or variant thereof in which one or more cysteines have been substituted for another amino acid, preferably serine. Examples of suitable linkers of this type are provided in SEQ ID NOs: 58-61.

Examples of single chain Fc polypeptides according to the present invention are provided for IgG1, 2, 3 and 4 in SEQ ID NOS: 8-13, 21-26, 34-39 and 47-52 respectively. See also FIG. 6 for examples of IgG1 sequences. The invention also extends to variants of these sequences as set out herein above. In one example the present invention provides a single chain Fc polypeptide comprising a sequence having at least 70% identity or similarity to any one of the sequences given in SEQ ID NOS: 8-13, 21-26, 34-39 and 47-52. In another example a single chain Fc polypeptide of the present invention comprises a sequence having at least 80% identity or similarity to any one of the sequences given in SEQ ID NOS: 8-13, 21-26, 34-39 and 47-52. In another example a single chain Fc polypeptide of the present invention comprises a sequence having at least 90% identity or similarity to any one of the sequences given in SEQ ID NOS: 8-13, 21-26, 34-39 and 47-52. In another example a single chain Fc polypeptide of the present invention comprises a sequence having at least 95% or 98% identity or similarity to any one of the sequences given in SEQ ID NOS: 8-13, 21-26, 34-39 and 47-52.

In one embodiment the single chain Fc polypeptide of the present invention further comprises a CH1 domain fused optionally via a hinge to the N-terminus of the first CH2 domain. Examples of suitable CH1 domains are provided in SEQ ID NOs 1, 14, 27 and 40.

The single chain Fc polypeptides of the present invention can be used in a number of applications, including therapeutic, diagnostic and research applications. Preferably the single chain Fc polypeptides of the present invention further comprise one or more other molecules which may be fused or otherwise linked at the N and/or C-terminus and/or elsewhere on the polypeptide. Such molecules include, but are not limited to, nucleic acids, small molecules, carbohydrates, proteins and peptides, including for example receptor proteins, antibodies and antibody fragments. The single-chain Fc polypeptide may be linked to another molecule, optionally via a linker (amino acid or chemical), by any suitable means known in the art, including for example, chemical conjugation, chemical cross-linking or genetic fusion. In one embodiment the single chain Fc polypeptide comprises a cysteine containing linker, such as an antibody hinge, at its N-terminus and one of these free cysteines is used as a site of attachment for another molecule, preferably a biologically active molecule as described below.

In one embodiment the single-chain Fc polypeptides of the present invention are used as an Fc tag, for example to aid protein purification and/or protein detection. Accordingly in one embodiment the single-chain Fc polypeptide further comprises at its N-terminus all or part of another protein. Such Fc fusions advantageously do not dimerise unlike currently available Fc fusions thus ensuring that the fusion protein remains monomeric. In certain applications, where it is desirable to be able to remove the Fc domain, for example after purification, the single-chain Fc polypeptide may be linked to another protein via a cleavable linker.

In one embodiment the single-chain Fc polypeptide of the present invention is linked at its N and/or C-terminus to a biologically active molecule. The biologically active molecule may be any protein or other suitable molecule, including nucleic acids, small molecules, carbohydrates, receptor proteins or immunoglobulins. Some examples of biologically active molecules include enzymes, antibody fragments, domain antibodies, single chain antibodies, aptamers, Microbodies™, binding agents based on protein scaffolds (see for example Nygren and Uhlen, 1997, Current Opinion in Structural Biology, 7, 463-469) versabodies, avimers, adnectins, anticalins, phylomers, aptamers, cyclic peptides, peptides, antiviral agents, hemostatic agents and cytokines and growth factors such as EPO, RANTES, interleukins such as IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, IL-8, IL-12, IL-13, IL-16 or IL-17, interferons such as interferon α, interferon β or interferon γ, tumour necrosis factor-α, tumor necrosis factor-β, colony stimulating factors such as G-CSF or GM-CSF.

In one embodiment the biologically active molecule brings the single-chain Fc polypeptide of the present invention into contact with a desired target, for example a target protein. In one embodiment the biologically active molecule binds to a desired target protein. In one example the target protein is a cell-associated protein, for example a cell surface protein on cells such as bacterial cells, yeast cells, T-cells, endothelial cells or tumour cells, or it may be a soluble protein. Target proteins may also be any medically relevant protein such as those proteins upregulated during disease or infection, for example receptors and/or their corresponding ligands. Particular examples of cell surface proteins include adhesion molecules, for example integrins such as β1 integrins e.g. VLA-4, E-selectin, P selectin or L-selectin, CD2, CD3, CD4, CD5, CD7, CD8, CD11a, CD11b, CD18, CD19, CD20, CD23, CD25, CD33, CD38, CD40, CD45, CDW52, CD69, CD134 (OX40), ICOS, BCMP7, CD137, CD27L, CD28, CD40L, CTLA-4, CD22, CDCP1, DPCR1, DPCR1, dudulin2, FLJ20584, FLJ40787, HEK2, KIAA0634, KIAA0659, KIAA1246, KIAA1455, LTBP2, LTK, MAL2, MRP2, nectin-like2, NKCC1, PTK7, RAIG1, TCAM1, SC6, BCMP101, BCMP84, BCMP11, DTD, carcinoembryonic antigen (CEA), human milk fat globulin (HMFG1 and 2), MHC Class I and MHC Class II antigens, and VEGF, and where appropriate, receptors thereof.

In one embodiment the target protein is a soluble protein. Soluble proteins include interleukins such as IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, IL-8, IL-12, IL-13, IL-16 or IL-17, viral proteins for example respiratory syncytial virus or cytomegalovirus proteins, immunoglobulins, such as IgE, interferons such as interferon α, interferon β or interferon γ, tumour necrosis factor-α, tumor necrosis factor-β, colony stimulating factors such as G-CSF or GM-CSF, and platelet derived growth factors such as PDGF-α, and PDGF-β and where appropriate receptors thereof.

In one embodiment the single-chain Fc polypeptides of the present invention may be used to functionally alter the activity of a particular protein to which the biologically active molecule binds. For example the single-chain Fc polypeptide may neutralize, antagonize or agonize the activity of a protein. In one embodiment the binding of the single-chain Fc polypeptide to a cell via the biologically active molecule results in cell killing e.g. via complement mediated cytotoxicity.

In one embodiment the biologically active molecule is a monovalent binding domain, in particular, a monovalent protein such as a receptor or fragment thereof or an immunoglobulin or fragment thereof.

In one embodiment the biologically active molecule is a receptor that may be naturally expressed on a cell surface or inside the cell. Examples of suitable receptors include, but are not limited to, viral receptors, cytokine receptors, growth factor receptors, hormone receptors and bacterial receptors. It will be appreciated that the term ‘receptor’ as used herein also includes suitable fragments of such receptors, an example of which includes the extracellular domain of a receptor. In one example the receptor is the human gp130 receptor or a cytokine binding fragment thereof, such as domain 1, 2 and/or 3. In one example the biologically active molecule comprises domain 1 of the gp130 receptor or a fragment thereof. In one example the biologically active molecule comprises amino acids 1 to 125 of SEQ ID NO:91. In one example the biologically active molecule comprises domain 2 and domain 3 of the gp130 receptor. In one example the biologically active molecule comprises domain 1, domain 2 and domain 3 of the gp130 receptor. It will also be appreciated that the term ‘receptor’ as used herein includes modified forms of naturally occurring receptors, including for example amino acid substitutions, additions or deletions. In one example a receptor comprising two chains may be produced as a single chain and linked to a single chain Fc polypeptide of the present invention. In one example the receptor may comprise all or part of the extracellular domains of the alpha and beta chains of the T cell receptor (TCR). Preferably these alpha and beta extracellular domains are linked in a single chain by a suitable linker which is in turn linked to a single chain Fc polypeptide of the present invention.

Preferably the monovalent binding protein is an antibody fragment. Examples of suitable antibody fragments include but are not limited to, scFv, Fab, Fab′, V_(HH), Fv, Vκ, VH, Vλ, epitope-binding fragments of any of the above. Examples of suitable antibody fragments include those described in Adair and Lawson, 2005. Therapeutic antibodies. Drug Design Reviews—Online 2(3):209-217, WO2005003169, WO2005003170 and WO2005003171.

An antibody fragment for use in the present invention can be derived from any class (e.g. IgG, IgE, IgM, IgD or IgA) or subclass of immunoglobulin molecule and may be obtained from any species including for example mouse, rat, shark, rabbit, pig, hamster, camel, llama, goat or human.

In one embodiment the antibody fragment is a monoclonal, humanized and/or chimeric antibody fragment.

Humanized antibodies are antibody molecules having one or more complementarity determining regions (CDRs) from a non-human species and a framework region from a human immunoglobulin molecule which optionally comprises one or more donor residues from the non-human species (see, for example, U.S. Pat. No. 5,585,089).

Chimeric antibodies have been genetically engineered so that the light and heavy chain genes are composed of immunoglobulin gene segments belonging to different species. Preferably the heavy and light chain constant regions are human and the variable regions are derived from another species.

Monoclonal antibodies may be prepared by any method known in the art such as the hybridoma technique (Kohler & Milstein, Nature, 1975, 256, 495-497), the trioma technique, the human B-cell hybridoma technique (Kozbor et al., Immuunology Today, 1983, 4, 72) and the EBV-hybridoma technique (Cole et al., “Monoclonal Antibodies and Cancer Therapy”, pp. 77-96, Alan R. Liss, Inc., 1985).

Antibodies may also be obtained by any other suitable method such as those described in Babcook, J. et al., Proc. Natl. Acad. Sci. USA, 1996, 93 (15), 7843-7848, WO 92/02551, WO2004/051268 and WO2004/106377.

An antibody fragment for use in the present invention may be obtained from any whole antibody, especially a whole monoclonal antibody, using any suitable enzymatic cleavage and/or digestion techniques, for example by treatment with pepsin. Alternatively antibody fragments may be prepared by the use of recombinant DNA techniques involving the manipulation and re-expression of DNA encoding antibody variable and/or constant regions. Standard molecular biology techniques may be used to modify, add or delete amino acids or domains as desired. Any alterations to the variable or constant regions are still encompassed by the terms ‘variable’ and ‘constant’ regions as used herein.

The methods for creating and manufacturing antibodies and antibody fragments are well known in the art (see for example, Boss et al., U.S. Pat. No. 4,816,397; Cabilly et al., U.S. Pat. No. 6,331,415; Shrader et al., WO 92/02551; Ward et al., 1989, Nature, 341, 544; Orlandi et al., 1989, Proc. Natl. Acad. Sci. USA, 86, 3833; Riechmann et al., 1988, Nature, 322, 323; Bird et al, 1988, Science, 242, 423; Queen et al., U.S. Pat. No. 5,585,089; Adair, WO91/09967; Mountain and Adair, 1992, Biotechnol. Genet. Eng. Rev, 10, 1-142; Verma et al., 1998, Journal of Immunological Methods, 216, 165-181).

Antibody fragments for use in the present invention may possess a native or a modified hinge region comprising one or more cysteines. The native hinge region is the hinge region normally associated with the C_(H)1 domain of the antibody molecule. A modified hinge region is any hinge that differs in length and/or composition from the native hinge region. Such hinges can include hinge regions from other species, such as human, mouse, rat, rabbit, shark, pig, hamster, camel, llama or goat hinge regions. Other modified hinge regions may comprise a complete hinge region derived from an antibody of a different class or subclass from that of the C_(H)1 domain. Thus, for instance, a C_(H)1 domain of class γ1 may be attached to a hinge region of class γ4. Alternatively, the modified hinge region may comprise part of a natural hinge or a repeating unit in which each unit in the repeat is derived from a natural hinge region. In a further alternative, the natural hinge region may be altered by converting one or more cysteine or other residues into neutral residues, such as serine or alanine, or by converting suitably placed residues into cysteine residues. By such means the number of cysteine residues in the hinge region may be increased or decreased. Other modified hinge regions may be entirely synthetic and may be designed to possess desired properties such as length, cysteine composition and flexibility.

A number of modified hinge regions have already been described for example, in U.S. Pat. No. 5,677,425, WO9915549, WO9825971 and WO2005003171 and these are incorporated herein by reference. In one example the protein for use in the present invention is a Fab′ fragment with a native or a modified hinge region.

In one example, one or more cysteines may be engineered into the antibody fragments of the present invention, for example to create surface exposed cysteine(s) (U.S. Pat. No. 5,219,996). Thus by using suitable engineering techniques the number of cysteines in an antibody fragment may be modified in order to provide a specific number of sites for example for effector molecule attachment.

In one embodiment the single chain-Fc polypeptide of the present invention further comprises an antibody fragment.

In one embodiment the antibody fragment is a single chain-Fv polypeptide. In one embodiment the single chain-Fc polypeptide of the present invention further comprises a single-chain Fv polypeptide. In one embodiment the C-terminus of the VH domain of the sc-Fv is genetically fused to the N-terminus of the first CH2 domain, optionally via one of the linkers described herein above. In one embodiment the C-terminus of the VL domain of the sc-Fv is genetically fused to the N-terminus of the first CH2 domain, optionally via one of the linkers described herein above.

In one embodiment the biologically active molecule is a Fab or Fab′ (See for example FIG. 1). In one embodiment the single chain-Fc polypeptide of the present invention further comprises an antibody Fab or Fab′ fragment. In one embodiment the C-terminus of the VH—CH1 chain of the Fab or Fab′ is genetically fused to the N-terminus of a single-chain Fc polypeptide of the present invention. In this embodiment the VL-CL chain of the Fab or Fab′ is linked to the VH—CH1 chain by a disulphide bond, preferably the native interchain disulphide bond. In one embodiment the C-terminus of the VL-CL chain of the Fab or Fab′ is genetically fused to the N-terminus of a single-chain Fc polypeptide of the present invention. In this embodiment the VH—CH1 chain of the Fab or Fab′ is linked to the VL-CL by a disulphide bond, preferably the native interchain disulphide bond.

The single chain Fc polypeptide of the present invention may have one or more effector molecules attached. Effector molecules may be attached by any suitable method, for example by chemical conjugation or genetic fusion.

The term ‘effector molecule’ as used herein includes, for example, antineoplastic agents, drugs, toxins (such as enzymatically active toxins of bacterial or plant origin and fragments thereof e.g. ricin and fragments thereof) biologically active proteins, for example enzymes, other antibody or antibody fragments, synthetic or naturally occurring polymers, nucleic acids and fragments thereof e.g. DNA, RNA and fragments thereof, radionuclides, particularly radioiodide, radioisotopes, chelated metals, nanoparticles and reporter groups such as fluorescent compounds or compounds which may be detected by NMR or ESR spectroscopy. It will be appreciated that an effector molecule may comprise a single effector molecule or two or more such molecules so linked as to form a single moiety that can be attached to a protein using the process of the present invention.

Particular antineoplastic agents include cytotoxic and cytostatic agents for example alkylating agents, such as nitrogen mustards (e.g. chlorambucil, melphalan, mechlorethamine, cyclosphophamide, or uracil mustard) and derivatives thereof, triethylenephosphoramide, triethylenethiophosphor-amide, busulphan, or cisplatin; antimetabolites, such as methotrexate, fluorouracil, floxuridine, cytarabine, mercaptopurine, thioguanine, fluoroacetic acid, or fluorocitric acid, antibiotics, such as bleomycins (e.g. bleomycin sulphate), doxorubicin, daunorubicin, mitomycins (e.g. mitomycin C), actionmycins (e.g. dactinomycin) plicamyin, calicheamicin and derivatives thereof, or esperamicin and derivatives thereof; mitotic inhibitors, such as etoposide, vincristine or vinblastine and derivatives thereof; alkaloids such as ellipticine; polyols such as taxicin-I or taxicin-II; hormones, such as androgens (e.g. dromostanolone or testolactone), progestins (e.g. megestrol acetate or medroxyprogesterone acetate), estrogens (e.g. dimethylstilbestrol diphosphate, polyestradiol phosphate or estramustine phosphate) or antiestrogens (e.g. tamoxifen); anthraquinones, such as mitoxantrone, ureas, such as hydroxyurea; hydrazines, such as procarbazine; or imidazoles, such as dacarbazine.

Chelated metals include chelates of di- or tripositive metals having a coordination number from 2 to 8 inclusive. Particular examples of such metals include technetium (Tc), rhenium (Re), cobalt (Co), copper (Cu), gold (Au), silver (Ag), lead (Pb), bismuth (Bi), indium (In), gallium (Ga), yttrium (Y), terbium (Tb), gadolinium (Gd), and scandium (Sc). In general the metal is preferably a radionuclide. Particular radionuclides include ^(99m)Tc, ¹⁸⁶Re, ¹⁸⁸Re, ⁵⁸Co, ⁶⁰Co, ⁶⁷Cu, ¹⁹⁵Au, ¹⁹⁹Au, ¹¹⁰Ag, ²⁰³Pb, ²⁰⁶Bi, ²⁰⁷Bi, ¹¹¹In, ⁶⁷Ga, ⁶⁸Ga, ⁸⁸Y, ⁹⁰Y, ¹⁶⁰Tb, ¹⁵³Gd and ⁴⁷Sc.

The chelated metal may be for example one of the above types of metal chelated with any suitable polyadentate chelating agent, for example acyclic or cyclic polyamines, polyethers, (e.g. crown ethers and derivatives thereof); polyamides; porphyrins; and carbocyclic derivatives.

In general, the type of chelating agent will depend on the metal in use. One particularly useful group of chelating agents in conjugates according to the invention, however, are acyclic and cyclic polyamines, especially polyaminocarboxylic acids, for example diethylenetriaminepentaacetic acid and derivatives thereof, and macrocyclic amines, e.g. cyclic tri-aza and tetra-aza derivatives (for example as described in International Patent Specification No. WO 92/22583); and polyamides, especially desferriox-amine and derivatives thereof.

Other effector molecules include other proteins, peptides and enzymes. Enzymes of interest include, but are not limited to, proteolytic enzymes, hydrolases, lyases, isomerases, transferases. Proteins, polypeptides and peptides of interest include, but are not limited to, immunoglobulins, albumin, toxins such as abrin, ricin A, pseudomonas exotoxin, or diphtheria toxin, a protein such as insulin, tumour necrosis factor, α-interferon, β-interferon, nerve growth factor, platelet derived growth factor or tissue plasminogen activator, a thrombotic agent or an anti-angiogenic agent, e.g. angiostatin or endostatin, or, a biological response modifier such as a lymphokine, interleukin-1 (IL-1), interleukin-2 (IL-2), interleukin-6 (IL-6), granulocyte macrophage colony stimulating factor (GM-CSF), granulocyte colony stimulating factor (G-CSF), nerve growth factor (NGF) or other growth factors.

Other effector molecules may include detectable substances useful for example in diagnosis. Examples of detectable substances include various enzymes, prosthetic groups, fluorescent materials, luminescent materials, bioluminescent materials, radioactive nuclides, positron emitting metals (for use in positron emission tomography), and nonradioactive paramagnetic metal ions. See generally U.S. Pat. No. 4,741,900 for metal ions which can be conjugated to antibodies for use as diagnostics. Suitable enzymes include horseradish peroxidase, alkaline phosphatase, beta-galactosidase, or acetylcholinesterase; suitable prosthetic groups include streptavidin, avidin and biotin; suitable fluorescent materials include umbelliferone, fluorescein, rhodamine red, rhodamine green, B-phycoerythrin, R-phycoerythrin, allophycosyanin, Texas red, Pacific blue, Marina blue, Oregon green and the Alexa Fluor series 350, 405, 430, 488, 500, 514, 532, 546, 555, 568, 594, 610, 633, 647, 660, 680, 700 and 750; suitable luminescent materials include luminol; suitable bioluminescent materials include luciferase, luciferin, and aequorin; and suitable radioactive nuclides include ¹²⁵I, ¹³¹I, ¹¹¹In and ⁹⁹Tc.

Synthetic or naturally occurring polymers for use as effector molecules include, for example optionally substituted straight or branched chain polyalkylene, polyalkenylene, or polyoxyalkylene polymers or branched or unbranched polysaccharides, e.g. a homo- or hetero-polysaccharide such as lactose, amylose, dextran, starch or glycogen. Particular optional substituents which may be present on the above-mentioned synthetic polymers include one or more hydroxy, methyl or methoxy groups. Particular examples of synthetic polymers include optionally substituted straight or branched chain poly(ethyleneglycol), poly(propyleneglycol), poly(vinylalcohol) or derivatives thereof, especially optionally substituted poly(ethyleneglycol) such as methoxypoly(ethyleneglycol) or derivatives thereof.

“Derivatives” as used herein is intended to include reactive derivatives, for example thiol-selective reactive groups such as an α-halocaraboxylic acid or ester, e.g. iodoacetamide, an imide, e.g. maleimide, a vinyl sulphone or disulphide malemides and the like. The reactive group may be linked directly or through a linker segment to the polymer. It will be appreciated that the residue of such a group will in some instances form part of the product as the linking group between the protein and the polymer.

It will be appreciated that one or more other domains or biologically active molecules may be genetically fused or otherwise conjugated to the C-terminus of the single-chain polypeptide.

In one embodiment the single-chain Fc polypeptide further comprises a transmembrane domain fused to the C-terminus of the single chain Fc polypeptide. The transmembrane domain allows the single-chain Fc polypeptides to be expressed on the surface of a cell. Accordingly, appropriate transmembrane domains may be used depending on the cell type of interest. A number of different transmembrane domains have been described, see for example WO97/23613, WO99/00494, WO99/57268, WO00/63374 and WO00/63373. Other examples of suitable transmembrane domains include the natural transmembrane domains with which immunoglobulins are expressed on the surface of B cells, see for example the sequences given in SEQ ID NOs: 65, 68, 71, 74, 77, 80, 83 and 86. In one embodiment the transmembrane domains are connected to the C-terminus of the single chain Fc polypeptide via a linker. In one embodiment this is the natural linker with which immunoglobulins are expressed on the surface of B cells, see for example the sequences given in SEQ ID NOs: 64, 67, 70, 73, 76, 79, 82 and 85.

In one embodiment the present invention provides a single-chain Fc polypeptide which further comprises a transmembrane domain and one or more signaling domains. In one embodiment the present invention provides a single-chain Fc polypeptide further comprising a transmembrane domain fused to the C-terminus, optionally via a linker, which is in turn fused at its C-terminus to one or more signaling domains. Suitable signaling domains are well known in the art and appropriate signaling and transmembrane domains may be chosen in order to obtain the desired expression and/or signaling in the cell in which the single-chain Fc is expressed.

In one example the intracellular domains are the natural intracellular domains with which immunoglobulins are expressed on the surface of B cells, see for example the sequences given in SEQ ID NOs: 66, 69, 72, 75, 78, 81, 84 and 87.

Examples of suitable signaling domains have also been described in WO97/23613, WO99/00494, WO99/57268, WO00/63372, WO00/63374, WO00/63373, WO01/32709, WO01/32866, WO01/32867, WO02/33101 and WO2004/039840.

In one embodiment where the single chain Fc polypeptide also comprises a biological molecule as described herein above, fused to its N-terminus, the single-chain Fc polypeptide can be used as a chimeric receptor protein. Such single-chain Fc polypeptides have the advantageous property that they do not dimerise on the surface of the cell and accordingly avoid inappropriate signaling in the absence of bound ligand.

The present invention also provides an isolated DNA sequence encoding any one of the single chain Fc polypeptides of the present invention. The DNA sequences of the present invention may comprise synthetic DNA, for instance produced by chemical processing, cDNA, genomic DNA or any combination thereof.

DNA sequences which encode a single chain Fc polypeptide of the present invention can be obtained by methods well known to those skilled in the art. For example, DNA sequences coding for part or all of the antibody Fc domains may be synthesized as desired from the determined DNA sequences or on the basis of the corresponding amino acid sequences. DNA coding for antibody Fc constant domains is widely available to those skilled in the art and can be readily synthesized on the basis of their known amino acid sequences.

Standard techniques of molecular biology may be used to prepare DNA sequences coding for the single chain Fc polypeptide of the present invention. Desired DNA sequences may be synthesized completely or in part using oligonucleotide synthesis techniques. Site-directed mutagenesis and polymerase chain reaction (PCR) techniques may be used as appropriate.

The present invention also relates to a cloning or expression vector comprising one or more DNA sequences of the present invention. Accordingly, provided is a cloning or expression vector comprising one or more DNA sequences encoding a single chain Fc polypeptide of the present invention. In one embodiment the cloning or expression vector comprises a single DNA sequence, encoding the entire single chain Fc polypeptide and optionally all or part of the biologically active molecule e.g. a scFv or V_(HH). In another embodiment the cloning or expression vector comprises two DNA sequences, for example the first DNA sequence encoding the single chain Fc polypeptide and one chain of biologically active molecule, eg. VH—CH1 and the second DNA sequence encoding a second chain of the biologically active molecule domain e.g. VL-CL. Preferably, a vector according to the present invention comprises an appropriate leader sequence, such as an antibody leader sequence.

General methods by which the vectors may be constructed, transfection methods and culture methods are well known to those skilled in the art. In this respect, reference is made to “Current Protocols in Molecular Biology”, 1999, F. M. Ausubel (ed), Wiley Interscience, New York and the Maniatis Manual produced by Cold Spring Harbor Publishing.

Also provided is a host cell comprising one or more cloning or expression vectors comprising one or more DNA sequences encoding a single chain Fc polypeptide of the present invention. Any suitable host cell/vector system may be used for expression of the DNA sequences encoding the single chain Fc polypeptide of the present invention. Bacterial, for example E. coli, and other microbial systems may be used or eukaryotic, for example mammalian, host cell expression systems may also be used. Suitable mammalian host cells include NS0, CHO, myeloma or hybridoma cells.

The present invention also provides a process for the production of a single chain Fc polypeptide according to the present invention comprising culturing a host cell containing a vector of the present invention under conditions suitable for leading to expression of protein from DNA encoding the single chain Fc polypeptide of the present invention, and isolating the single chain Fc polypeptide.

The single chain Fc polypeptide may comprise only a single chain and where this is expressed alone or as a genetic fusion to the biologically active molecule only a single polypeptide coding sequence needs to be used to transfect the host cells for example, scFvscFc. For production of single-chain Fc polypeptides comprising a biologically active molecule which comprises two or more chains the cell line may be transfected with two or more vectors, a first vector encoding the single chain Fc polypeptide fused to a first chain of the biologically active molecule (e.g. VH—CH1) and a second vector encoding a second chain of the biologically active molecule (e.g. VL-CL). Alternatively, a single vector may be used, the vector including sequences encoding both chains of the biologically active molecule where one of the chains is fused to the single chain Fc polypeptide.

Once produced the single-chain Fc polypeptide of the present invention may be purified where necessary using any suitable method known in the art including, for example chromatography techniques such as ion exchange, size exclusion, protein A or hydrophobic interaction chromatography.

The size of the single-chain Fc polypeptide may be confirmed by conventional methods known in the art such as size exclusion chromatography and non-reducing SDS-PAGE. Such techniques can be used to confirm that the scFc has not dimerized. If dimers are detected then the monomeric single-chain Fc polypeptides may be purified away from the dimeric species using conventional chromatography techniques as described above.

The functionality of the single-chain Fc polypeptides of the present invention may be determined using any suitable method known in the art depending on the effector functions required, including those methods provided in the Examples. Suitable assays include Fc receptor binding assays, complement fixing assays, co-stimulation assays, cell killing assays, cytotoxicity assays and cytostatis assays. In addition, half-life can be measured using suitable pharmacokinetic methods known in the art.

Further, where the biologically active molecule binds to a surface protein and targets the single-chain Fc polypeptide to this surface expressed protein, other functional assays, such as cell killing assays (e.g. complement mediated cytotoxicity assays) may also be used. Accordingly, suitable functional assays may be readily established by one skilled in the art to determine whether the desired function is achieved.

The single chain Fc polypeptides of the present invention are useful in the treatment and/or prophylaxis of disease. Accordingly, the present invention also provides a pharmaceutical or diagnostic composition comprising a single chain Fc polypeptide of the present invention in combination with one or more of a pharmaceutically acceptable excipient, diluent or carrier. Accordingly, provided is the use of a single chain Fc polypeptide of the invention for the manufacture of a medicament. The composition will usually be supplied as part of a sterile, pharmaceutical composition that will normally include a pharmaceutically acceptable carrier. A pharmaceutical composition of the present invention may additionally comprise a pharmaceutically-acceptable adjuvant.

The present invention also provides a process for preparation of a pharmaceutical or diagnostic or research reagent composition comprising adding and mixing the single chain Fc polypeptide of the present invention together with one or more of a pharmaceutically acceptable excipient, diluent or carrier.

The single-chain Fc polypeptide may be the sole active ingredient in the pharmaceutical or diagnostic composition or may be accompanied by other active ingredients including for example other antibody or non-antibody ingredients including for example anti-inflammatories and chemotherapeutic agents.

The pharmaceutical compositions preferably comprise a therapeutically effective amount of the single-chain Fc polypeptide of the invention. The term “therapeutically effective amount” as used herein refers to an amount of a therapeutic agent needed to treat, ameliorate or prevent a targeted disease or condition, or to exhibit a detectable therapeutic or preventative effect. For any single-chain Fc polypeptide, the therapeutically effective amount can be estimated initially either in cell culture assays or in animal models, usually in rodents, rabbits, dogs, pigs or primates. The animal model may also be used to determine the appropriate concentration range and route of administration. Such information can then be used to determine useful doses and routes for administration in humans.

The precise therapeutically effective amount for a human subject will depend upon the severity of the disease state, the general health of the subject, the age, weight and gender of the subject, diet, time and frequency of administration, drug combination(s), reaction sensitivities and tolerance/response to therapy. This amount can be determined by routine experimentation and is within the judgement of the clinician. Generally, a therapeutically effective amount will be from 0.01 mg/kg to 50 mg/kg, preferably 0.1 mg/kg to 20 mg/kg. Pharmaceutical compositions may be conveniently presented in unit dose forms containing a predetermined amount of an active agent of the invention per dose.

Compositions may be administered individually to a patient or may be administered in combination (e.g. simultaneously, sequentially or separately) with other agents, drugs or hormones.

The dose at which the single-chain Fc polypeptide of the present invention is administered depends on the nature of the condition to be treated, the extent of the inflammation present and on whether the antibody molecule is being used prophylactically or to treat an existing condition.

The frequency of dose will depend on the half-life of the single-chain Fc polypeptide and the duration of its effect. If the single-chain Fc polypeptide has a short half-life (e.g. 2 to 10 hours) it may be necessary to give one or more doses per day. Alternatively, if the single-chain Fc polypeptide has a long half life (e.g. 2 to 15 days) it may only be necessary to give a dosage once per day, once per week or even once every 1 or 2 months.

The pharmaceutically acceptable carrier should not itself induce the production of antibodies harmful to the individual receiving the composition and should not be toxic. Suitable carriers may be large, slowly metabolized macromolecules such as proteins, polypeptides, liposomes, polysaccharides, polylactic acids, polyglycolic acids, polymeric amino acids, amino acid copolymers and inactive virus particles.

Pharmaceutically acceptable salts can be used, for example mineral acid salts, such as hydrochlorides, hydrobromides, phosphates and sulphates, or salts of organic acids, such as acetates, propionates, malonates and benzoates.

Pharmaceutically acceptable carriers in therapeutic compositions may additionally contain liquids such as water, saline, glycerol and ethanol. Additionally, auxiliary substances, such as wetting or emulsifying agents or pH buffering substances, may be present in such compositions. Such carriers enable the pharmaceutical compositions to be formulated as tablets, pills, dragees, capsules, liquids, gels, syrups, slurries and suspensions, for ingestion by the patient.

Preferred forms for administration include forms suitable for parenteral administration, e.g. by injection or infusion, for example by bolus injection or continuous infusion. Where the product is for injection or infusion, it may take the form of a suspension, solution or emulsion in an oily or aqueous vehicle and it may contain formulatory agents, such as suspending, preservative, stabilizing and/or dispersing agents. Alternatively, the single-chain Fc polypeptide may be in dry form, for reconstitution before use with an appropriate sterile liquid.

Once formulated, the compositions of the invention can be administered directly to the subject. The subjects to be treated can be animals. However, it is preferred that the compositions are adapted for administration to human subjects.

The pharmaceutical compositions of this invention may be administered by any number of routes including, but not limited to, oral, pulmonary, intravenous, intramuscular, intra-arterial, intramedullary, intrathecal, intraventricular, transdermal, transcutaneous (for example, see WO 98/20734), subcutaneous, intraperitoneal, intranasal, enteral, topical, sublingual, intravaginal or rectal routes. Hyposprays and nebulisers may also be used to administer the pharmaceutical compositions of the invention. Typically, the therapeutic compositions may be prepared as injectables, either as liquid solutions or suspensions. Solid forms suitable for solution in, or suspension in, liquid vehicles prior to injection may also be prepared.

Direct delivery of the compositions will generally be accomplished by injection, subcutaneously, intraperitoneally, intravenously or intramuscularly, or delivered to the interstitial space of a tissue. The compositions can also be administered into a lesion. Dosage treatment may be a single dose schedule or a multiple dose schedule.

It will be appreciated that the active ingredient in the composition will be a single-chain Fc polypeptide. As such, it will be susceptible to degradation in the gastrointestinal tract. Thus, if the composition is to be administered by a route using the gastrointestinal tract, the composition will need to contain agents which protect the single-chain Fc polypeptide from degradation but which release the single-chain Fc polypeptide once it has been absorbed from the gastrointestinal tract.

A thorough discussion of pharmaceutically acceptable carriers is available in Remington's Pharmaceutical Sciences (Mack Publishing Company, N.J. 1991).

It is also envisaged that the single-chain Fc polypeptide of the present invention will be administered by use of gene therapy. In order to achieve this, DNA sequences encoding the single chain Fc polypeptide under the control of appropriate DNA components are introduced into a patient such that the single chain Fc polypeptide is expressed from the DNA sequence(s) and assembled in situ. Alternatively the single-chain Fc polypeptide may be transfected ex vivo into appropriate cells, such as T cells. Examples of suitable methods for ex vivo transfections are described in WO2004/039840.

The present invention also provides a single-chain Fc polypeptide for use in the treatment or prophylaxis of a pathological disorder that is selected from the group consisting of infections (viral, bacterial, fungal and parasitic), endotoxic shock associated with infection, arthritis, rheumatoid arthritis, asthma, pelvic inflammatory disease, Alzheimer's Disease, Crohn's disease, Peyronie's Disease, coeliac disease, gallbladder disease, Pilonidal disease, peritonitis, psoriasis, vasculitis, surgical adhesions, stroke, Type I Diabetes, lyme arthritis, meningoencephalitis, immune mediated inflammatory disorders of the central and peripheral nervous system such as multiple sclerosis and Guillain-Barr syndrome, other autoimmune disorders, pancreatitis, trauma (surgery), graft-versus-host disease, transplant rejection, cancer (both solid tumours such as melanomas, hepatoblastomas, sarcomas, squamous cell carcinomas, transitional cell cancers, ovarian cancers and hematologic malignancies and in particular acute myelogenous leukaemia, chronic myelogenous leukemia, gastric cancer and colon cancer), heart disease including ischaemic diseases such as myocardial infarction as well as atherosclerosis, intravascular coagulation, bone resorption, osteoporosis, periodontitis and hypochlorhydia.

Preferably the present invention provides a single-chain Fc polypeptide for use in the control of inflammatory diseases and cancer. Preferably, the single-chain Fc polypeptide can be used to reduce the inflammatory process or cancer or to prevent the inflammatory process or cancer.

EXAMPLES

The present invention will now be described by way of example, in which reference is made to:

FIG. 1( a)-(c): A diagrammatic representation of three examples of single chain Fc polypeptide according to the present invention which comprise an antibody Fab fragment and in which a linker connects the C-terminus of the first CH3 domain and the N-terminus of the second CH2 domain.

FIG. 2( a)-(c): A diagrammatic representation of three examples of single chain Fc polypeptide which comprise an antibody Fab fragment and in which a linker connects the C-terminus of the first CH2 domain to the N-terminus of the second CH2 domain and another linker connects the C-terminus of the first CH3 domain to the N-terminus of the second CH3 domain.

FIG. 3( a)-(c): A diagrammatic representation of three examples of single chain Fc polypeptide which comprise an antibody Fab fragment and in which:

(a) a linker connects the C-terminus of the first CH4 domain to the N-terminus of the second CH2 domain.

(b) a first linker connects the C-terminus of the first CH2 domain to the N-terminus of the second CH2 domain, a second linker connects the C-terminus of the second CH2 domain to the N-terminus of the first CH3 domain and a third linker connects the C-terminus of the first CH4 domain to the N-terminus of the second CH3 domain.

(c) a first linker connects the C-terminus of the first CH3 domain to the N-terminus of the second CH2 domain, a second linker connects the C-terminus of the second CH3 domain to the N-terminus of the first CH4 domain and a third linker connects the C-terminus of the first CH4 domain to the N-terminus of the second CH4 domain.

FIGS. 4 a and 4 b: demonstrate that the single chain Fc polypeptides bind to antigen recombinantly expressed on the surface of NS0 cells (FIG. 4 a) and naturally expressed on the surface of activated T cells (FIG. 4 b).

FIGS. 5 a and b: show the ability of the single chain Fc polypeptides to induce cytotoxicity of NS0 cells in the presence of complement (a) but not in the absence of complement (b).

FIGS. 5 c and 5 d: show the ability of the single chain Fc polypeptides to induce complement-dependent cytotoxicity of activated T cells.

FIG. 6: Example sequences of single chain Fc polypeptides derived from IgG1. Hinge sequences are in italics and linkers are underlined.

-   -   (a) format as shown in FIG. 1( a)     -   (b) format as shown in FIG. 1( b)     -   (c) format as shown in FIG. 1( c)     -   (d) format as shown in FIG. 2( a)     -   (e) format as shown in FIG. 2( b)     -   (f) format as shown in FIG. 2( c)

EXAMPLE 1

Three murine single chain Fc polypeptides comprising a biologically active molecule at the N-terminus were designed in which the biologically active molecule was an antibody Fab fragment. The variable regions of the Fab fragment were derived from murine antibody, Mox46, that binds to a cell surface protein antigen. The Fc domains were derived from murine IgG2a and the three different versions of these domains are shown below. The linker sequences are underlined. Hinge sequences are in italics and where these constitute part of the linker sequence they are in italics and underlined.

Version 1 SEQ ID NO:88 (format as illustrated in FIG. 2 b). The cysteines in the hinge between CH1 and CH2 have been substituted for serines.

EPRGPTIKPSPPSKSPAPNLLGGPSVFIFPPKIKDVLMISLSPIVTCVVV DVSEDDPDVQISWFVNNVEVHTAQTQTHREDYNSTLRVVSALPIQHQDWM SGKEFKCKVNNKDLPAPIERTISKPKGGGGSGGGGSGGGGSGGGGSGGGG SAPNLLGGPSVFIFPPKIKDVLMISLSPIVTCVVVDVSEDDPDVQISWFV NNVEVHTAQTQTHREDYNSTLRVVSALPHQHQDWMSGKEFKCKVNNKDLP APIERTISKPKGSVRAPQVYVLPPPEEEMTKKQVTLTCMVTDFMPEDIYV EWTNNGKTELNYKNTEPVLDSDGSYFMYSKLRVEKKNWVERNSYSCSVVH EGLHNHHTTKSFSRTPGKGGGGSGGGGSGGGGSGGGGSGGGGSGSVRAPQ VYLPPPEEEMTKKQVTLTCMVTDFMPEDIYVEWTNNGKTELNYKNTEPVL DSDGSYFMYSKLRVEKKNWVERNSYSCSVVHEGLHNHHTTKSFSRTPGK

Version 2 SEQ ID NO: 89 (format as illustrated in FIG. 2 a)

EPRGPTIKPCPAPNLLGGPSVFIFPPKIKDVLMISLSPIVTCVVDVSEDD PDVQISWFVNVEVHTAQTQTHREDYNSTLRVVSALPIQHQDWMSGKEFKC KVNNKDLPAPIERTISKPKGGGGSGGGGSGGGGSGGGGSGGGGSEPRGPT IKPCP APNLLGGPSVFIFPPKIKDVLMISLSPIVTCVVVDVSEDDPDVQI SWFVNNVEVHTAQTQTHREDYNSTLRVVSALPIQHQDWMSGKEFKCKVNN KDLPAPIERTISKPKGSVRAPQVYVLPPPEEEMTKKQVTLTCMVTDFMPE DIYVEWTNNGKTELNYKNTEPVLDSDGSYFMYSKLRVEKKNWVERNSYSC SVVHEGLHNHHTTKSFSRTPGKGGGGSGGGGSGGGGSGGGGSGGGGSGSV RAPQVYVLPPPEEEMTKKQVTLTCMVTDFMPEDIYVEWTNNGKTELNYKN TEPVLDSDGSYFMYSKLRVEKKNWVERNSYSCSVVHEGLHNHHTTKSFSR TPGK

Version 3 SEQ ID NO: 90 (format as illustrated in FIG. 1 a). Linker comprises a truncated hinge ‘PCP’.

EPRGPTIKPCPAPNLLGGPSVFIFPPKIKDVLMISLSPIVTCVVVDVSED DPDVQISWFVNNVEVHTAQTQTHREDYNSTLRVVSALPIQHQDWMSGKEF KCKVNNKDLPAPIERTISKPKGSVRAPQVYVLPPPEEEMTKKQVTLTCMV TDFMPEDIYVEWTNNGKTELNYKNTEPVLDSDGSYFMYSKLRVEKKNWVE RNSYSCSVVHEGLHNHHTTKSFSRTPGKGGSSTASGSGSGGSGTAGSSGG AGSSGGSTTAGGSASGSGSTGSGTGGASSGGASGASGPCPAPNLLGGPSV FIFPPKIKDVLMISLSPIVTCVVVDVSEDDPDVQISWFVNNVEVHTAQTQ THREDYNSTLRVVSALPIQHQDWMSGKEFKCKVNNKDLPAPIERTISKPK GSVRAPQVYVLPPPEEEMTKKQVTLTCMVTDFMPEDIYVEWTNNGKTELN YKNTEPVLDSDGSYFMYSKLRVEKKNWVERNSYSCSVVHEGLHNHHTTKS FSRTPGK

The DNA encoding each of the single chain Fc polypeptides was synthesized with the same biologically active molecule at the N-terminus i.e. the VHCH1 domain from antibody MOX46.

The single chain Fc polypeptides comprising versions 1, 2 and 3 above were expressed in a pVAX vector (Invitrogen) in HEK293 cells (a human embryonic kidney epithelial cell line) using an antibody leader sequence (from mouse antibody B72.3 (Whittle et al., 1987, Protein Eng. 1(6) 499-505)). The VLCL chain of the MOX46 Fab fragment was produced in the same cell but in a separate vector. The resulting single chain Fc polypeptides were purified using protein A.

EXAMPLE 2 Antigen Binding

The ability of the single-chain Fc polypeptides (versions 1 and 3) to bind to antigen was compared to the same antibody variable regions (from the MOX46 antibody) expressed in a murine IgG1 framework and an irrelevant IgG. Recombinant NSO cells expressing the antigen on their surface (5×10⁵) were incubated with 100 μl of the single chain Fc polypeptides for 30 minutes at 4° C. The control was MOPC21 which was titrated from 5 μg/ml down in 1/3 dilutions. The MOX46 IgG and the single-chain Fc constructs were titrated in 1/3 dilutions. The cells were washed twice in Dulbecco's PBS containing 5% FCS and 0.1% sodium azide and then 100 μl of anti-mouse heavy and light chain PE labelled (Jackson) antibody diluted 1/250 was added for 30 minutes at 4° C. The cells were washed once more as before and analyzed by flow cytometry.

Both of the single-chain Fc constructs tested bound antigen (1.1 and 3.1), as did the MOX46 IgG. The irrelevant control did not bind to the antigen. See FIG. 4 a.

The ability of the single chain Fc polypeptides (versions 1, 2 and 3) to bind antigen was also tested using the methods described above however primary activated T cells which naturally express the antigen on their surface were used instead of recombinant NS0 cells. The primary activated T cells were produced as follows: 1×10⁶ D011 splenocytes were cultured with 200 ng/ml ovalbumin peptide 323-329 for 3 days, washed and resuspended in twice the volume of medium for a further 2 days. The activated cells were then purified by negatively isolating the CD4 T cells.

All three single-chain Fc constructs bound antigen, as did the MOX46 IgG. The irrelevant control did not bind to the antigen. See FIG. 4 b.

EXAMPLE 3 Fc Receptor Binding

The ability of the single-chain Fc versions 1 and 3 to bind to Fc receptors CD64 (FcγRII) and CD32 (FcγRI) was determined by BIAcore. CD64 and CD32 were immobilized (approx 1000RU each) by amine coupling chemistry on flow cells 2 and 3 (respectively) of a standard CM5 Biacore chip. Flow cell 1 was set up as a reference flow cell to check for background binding. The single-chain Fc proteins were then injected in sequence over the chip to look for binding activity. All samples were run undiluted and at 1:2 and 1:5 dilutions. Background binding was insignificant with all samples.

Both versions 1 and 3 of the single-chain Fc were found to bind to both CD64 and CD32.

EXAMPLE 4 Complement-Dependent Cytotoxicity Assay using Recombinant NS0 Cells

Single-chain Fc versions 1 and 3 were tested for their ability to cause complement-mediated cytotoxicity of cells to which they were bound.

A recombinant NS0 line expressing the relevant antigen on its surface (5×10⁶) cells/ml media were mixed with 50 μl/ml baby rabbit complement (Serotec C12CA). Prior to use, the complement was reconstituted with 2 ml ice cold tissue culture grade distilled water. It was used within one hour of reconstitution and was maintained on ice until use. The agents tested were at a concentration of 2 μg/ml and plated onto a 96 well plate (Costar) in 100 μl volumes in duplicate. 100 μl of the cell/complement mix was added per well and the plate incubated at 37° C. for 4 hours. Cytotoxicity was assessed by uptake of the vital stain, propidium iodide (PI) by FACS. A stock solution of 20 mg/ml PI (Molecular Probes P-1304MP) was prepared in distilled water and then diluted in RPMI 1640 to give a final concentration in the well of 3 μg/ml. The cells were incubated for 10 min at RT in the dark, before being analyzed by flow cytometry.

FIG. 5 a (with complement) and FIG. 5 b (without complement) show that the both versions 1 and 3 of the single-chain Fc polypeptides (1.1 and 3.1) induce complement-dependent cytotoxicity.

EXAMPLE 5 Complement-Dependent Cytotoxicity Assay using Activated T Cells

(i) Single chain Fc versions 1, 2 and 3 were tested for their ability to cause complement-mediated cytotoxicity of activated T cells which express the antigen bound by the MOX46 antibody on their surface. The methods used were as described in Example 4 except primary activated T cells were used instead of NS0 cells and these were produced as described in Example 2.

% specific lysis of cells was calculated as follows:

% PI positive cells in experimental condition−background % PI positive cells

maximum % PI positive cells (lysis buffer)−background % PI positive cells

All three versions of the single chain Fc polypeptides were found to induce complement-dependent cytotoxicity (FIG. 5 c).

(ii) Another single chain Fc polypeptide (version 3) comprising an antibody Fab fragment derived from murine antibody, 495, that binds to a different cell surface protein antigen was produced as both an IgG1 and IgG2a format using murine Fc regions. The ability of these scFc proteins to cause complement-mediated cytotoxicity of activated T cells which express the antigen bound by the 495 antibody on their surface was tested. The methods used were as described in Example 4 except primary activated T cells were used which were produced as described in Example 2.

FIG. 5 d clearly illustrates that as expected only the IgG2a format of the single chain Fc and the IgG2b format of the whole antibody 495 were able to induce complement-dependent cytotoxicity. The IgG1 formats were unable to induce complement-dependent cytotoxicity.

EXAMPLE 6 Receptor-scFc Fusion

The human gp130 receptor domain 1 was cloned as a single chain Fc (mouse gamma 1) fusion protein using the single chain Fc format illustrated in FIG. 1 a. The sequence of the fusion protein is shown below.

Gp130 domain 1 scFc fusion protein (SEQ ID NO:91)

KLATMSVPTQ VLGLLLLWLT DARCELLDPC GYISPESPVV QLHSNFTAVC VLKEKCMDYF HVNANYIVWK TNHFTIPKEQ YTIINRTASS VTFTDIASLN IQLTCNILTF GQLEQNVYGI TIISGSSAVP RDGGSKPGIC TVPEVSSVFI FPPKPKDVLT ITLTPKVTCV VVDISKDDPE VQFSWFVDDV EVHTAQTQPR EEQFNSTFRS VSELPIMHQD WLNGKEFKCR VNSAAFPAPI EKTISKTKGR PKAPQVYTIP PPKEQMAKDK VSLTCMITDF FPEDITVEWQ WNGQPAENYK NTQPIMDTDG SYFVYSKLNV QKSNWSAGNT FTCSVLHEGL HNHHTEKSLS HSPGKGGSST ASGSGSGGSG TAGSSGGAGS SGGSTTAGGS ASGSGSTGSG TGGASSGGAS GASGVPRDGG SKPGICT VPE VSSVFIFPPK PKDVLTITLT PKVTCVVVDI SKDDPEVQFS WFVDDVEVHT AQTQPREEQF NSTFRSVSEL PIMHQDWLNG KEFKCRVNSA AFPAPIEKTI SKTKGRPKAP QVYTIPPPKE QMAKDKVSLT CMITDFFPED ITVEWQWNGQ PAENYKNTQP IMDTDGSYFV YSKLNVQKSN WEAGNTFTCS VLHEGLHNHH TEKSLSHSPG K*

The sequence in bold represents the gp130 receptor domain 1 (amino acids 1 to 125 of SEQ ID NO:91). The linker sequence is underlined. Hinge sequences are in italics and where they constitute part of the linker they are in italics and underlined. The sequence ‘SSA’ between the C-terminus of the gp130 domain 1 and the first hinge sequence are amino acids required to introduce the necessary Xho1 restriction site for cloning purposes.

The constructs were transiently expressed in a mammalian cell system (CHO L761) using a pVAX vector and the B72.3 mouse signal sequence. A western blot was 

1. A single chain Fc polypeptide comprising two CH2 domains and two CH3 domains characterized in that said CH2 and CH3 domains form a functional Fc domain within the polypeptide chain.
 2. A single chain Fc polypeptide according to claim 1 in which a first CH2 domain is dimerized with a second CH2 domain and a first CH3 domain is dimerized with a second CH3 domain within the polypeptide chain.
 3. A polypeptide according to claim 2 in which, in N— to C-terminal sequence a first CH2 domain is linked at its C-terminus to the N-terminus of a first CH3 domain, optionally via a linker, and said first CH3 domain is linked at its C-terminus via a linker to the N-terminus of a second CH2 domain which is linked at its C-terminus to the N-terminus of said second CH3 domain, optionally via a linker.
 4. A polypeptide according to claim 2 in which, in N— to C-terminal sequence, a first CH2 domain is linked at its C-terminus via a linker to the N-terminus of a second CH2 domain and said second CH2 domain is linked at its C-terminus to the N-terminus of a first CH3 domain, optionally via a linker, and said first CH3 domain is linked at its C-terminus to the N-terminus of a second CH3 domain via a linker.
 5. A polypeptide according to claim 2 which further comprises two CH4 domains which are dimerized to each other.
 6. A polypeptide according to claim 3 in which the linker between the C-terminus of the first CH3 domain and the N-terminus of the second CH2 domain is between 30 and 130 amino acids in length, and optionally comprises one or more amino acids selected from glycine, serine, alanine and threonine.
 7. A polypeptide according to claim 4 in which the linker between the C-terminus of the first CH2 domain and the N-terminus of the second CH2 domain is between 15 and 90 amino acids in length, and optionally comprises one or more amino acids selected from glycine, serine, alanine and threonine.
 8. A polypeptide according to claim 4 in which the linker between the C-terminus of the first CH3 domain and the N-terminus of the second CH3 domain is between 15 and 50 amino acids in length, and optionally comprises one or more amino acids selected from glycine, serine, alanine and threonine.
 9. (canceled)
 10. A polypeptide according to claim 6 in which the linker comprises the sequence given in SEQ ID NO:62.
 11. A polypeptide according to claim 7 in which the linker comprises the sequence given in SEQ ID NO:63.
 12. A polypeptide according to claim 8 in which the linker comprises the sequence given in SEQ ID NO:63.
 13. A polypeptide according to claim 10 in which the linker comprises one or more cysteine residues.
 14. A polypeptide according to claim 13 in which the linker comprises all or part of an antibody hinge sequence or a modified antibody hinge sequence.
 15. A polypeptide according to claim 14 in which the linker comprises an antibody hinge sequence selected from the sequence given in SEQ ID NO:53, SEQ ID NO:54, SEQ ID NO:55, SEQ ID NO:56, SEQ ID NO:57, SEQ ID NO:58, SEQ ID NO:59, SEQ ID NO:60 or SEQ ID NO:61.
 16. A polypeptide according to claim 6 wherein the linker comprises the sequences given in SEQ ID NO:62 and SEQ ID NO:53.
 17. A polypeptide according to claim 7 wherein the linker comprises the sequence given in SEQ ID NO:63 and SEQ ID NO:53.
 18. A polypeptide according to claim 1 in which each CH2 domain comprises the sequence given in SEQ ID NO:2 or SEQ ID NO:15 or SEQ ID NO:28 or SEQ ID NO:41.
 19. A polypeptide according to claim 1 in which each CH3 domain comprises the sequence given in SEQ ID NO:3 or SEQ ID NO:16 or SEQ ID NO:29 or SEQ ID NO:42.
 20. A polypeptide according to claim 1 in which each CH2 domain has at least 80% identity or similarity to a sequence given in claim 18 and each CH3 domain has at least 80% identity or similarity to a sequence given in claim
 19. 21. A polypeptide according to claim 1 in which the C-terminus of the second CH3 domain or CH4 domain, where present, is linked, optionally via a linker, to a transmembrane domain.
 22. The polypeptide according to claim 21 wherein the C-terminus of the transmembrane domain is linked to the N-terminus of a signalling domain, optionally via a linker.
 23. A single chain Fc polypeptide according to claim 1 which is linked to one or more biologically active molecules.
 24. A single chain Fc polypeptide according to claim 23 wherein the biologically active molecules are selected from a drug, a carbohydrate, a receptor or an antibody fragment.
 25. A single chain Fc polypeptide according to claim 23 wherein a biologically active molecule is linked to the N-terminus of the first CH2 domain of the single chain Fc polypeptide.
 26. A single chain Fc polypeptide according to claim 25 in which the biologically active molecule and the single chain Fc polypeptide are linked by a peptide linker of between 1 and 100 amino acids in length and optionally comprises a cysteine residue.
 27. (canceled)
 28. A single chain Fc polypeptide according to claim 26 wherein the linker comprises an antibody hinge sequence selected from the sequence given in SEQ ID NO:53, SEQ ID NO:54, SEQ ID NO:55, SEQ ID NO:56, SEQ ID NO:57, SEQ ID NO:58, SEQ ID NO:59, SEQ ID NO:60 or SEQ ID NO:61.
 29. A single chain Fc polypeptide according to claim 1 comprising the sequence given in SEQ ID NO:8, SEQ ID NO:9, SEQ ID NO:10, SEQ ID NO:11, SEQ ID NO:12, SEQ ID NO:13, SEQ ID NO:21, SEQ ID NO:22, SEQ ID NO:23, SEQ ID NO:24, SEQ ID NO:25, SEQ ID NO:26, SEQ ID NO:34, SEQ ID NO:35, SEQ ID NO:36, SEQ ID NO:37, SEQ ID NO:38, SEQ ID NO:39, SEQ ID NO:47, SEQ ID NO:48, SEQ ID NO:49, SEQ ID NO:50, SEQ ID NO:51 or SEQ ID NO:52.
 30. A single chain Fc polypeptide according to claim 1 comprising a sequence having at least 80% identity or similarity to any one of SEQ ID NO:8, SEQ ID NO:9, SEQ ID NO:10, SEQ ID NO:11, SEQ ID NO:12, SEQ ID NO:13, SEQ ID NO:21, SEQ ID NO:22, SEQ ID NO:23, SEQ ID NO:24, SEQ ID NO:25, SEQ ID NO:26, SEQ ID NO:34, SEQ ID NO:35, SEQ ID NO:36, SEQ ID NO:37, SEQ ID NO:38, SEQ ID NO:39, SEQ ID NO:47, SEQ ID NO:48, SEQ ID NO:49, SEQ ID NO:50, SEQ ID NO:51, or SEQ ID NO:52.
 31. (canceled)
 32. A single chain Fc polypeptide according to claim 24 wherein the biologically active molecule is an antibody fragment, and said antibody fragment is selected from VHH, VH, VL, VH—CH1, VL-CL, Fab, Fab′ or a scFv.
 33. A single chain Fc polypeptide according to claim 32 wherein the antibody fragment is a Fab and the C-terminus of the VH—CH1 chain of the Fab is genetically fused to the N-terminus of the single chain Fc polypeptide and the VL-CL chain of the Fab is linked to the VH—CH1 chain by a disulphide bond.
 34. A single chain Fc polypeptide according to claim 23 wherein the biologically active molecule comprises one or more domains of the human gp130 receptor or fragments thereof.
 35. A single chain Fc polypeptide according to claim 34 that comprises domain 1 of the human gp130 receptor or a fragment thereof.
 36. A single chain Fc polypeptide according to claim 1 to which one or more effector molecules is attached.
 37. An isolated DNA sequence encoding the single chain Fc polypeptide according to claim
 1. 38. A cloning or expression vector comprising one or more DNA sequences according to claim
 37. 39. A host cell comprising one or more cloning or expression vectors according to claim
 38. 40. A process for the production of the single chain Fc polypeptide of claim 1 comprising culturing the host cell of claim 39 and isolating the single chain Fc polypeptide.
 41. A pharmaceutical composition comprising a single chain Fc polypeptide according claim 1, in combination with one or more of a pharmaceutically acceptable excipient, diluent or carrier.
 42. A pharmaceutical composition according to claim 41, additionally comprising other active ingredients.
 43. A polypeptide according to claim 11 in which the linker comprises one or more cysteine residues.
 44. A polypeptide according to claim 12 in which the linker comprises one or more cysteine residues.
 45. A polypeptide according to claim 43 in which the linker comprises all or part of an antibody hinge sequence or a modified antibody hinge sequence.
 46. A polypeptide according to claim 44 in which the linker comprises all or part of an antibody hinge sequence or a modified antibody hinge sequence.
 47. A polypeptide according to claim 45 in which the linker comprises an antibody hinge sequence selected from the sequence given in SEQ ID NO:53, SEQ ID NO:54, SEQ ID NO:55, SEQ ID NO:56, SEQ ID NO:57, SEQ ID NO:58, SEQ ID NO:59, SEQ ID NO:60 or SEQ ID NO:61.
 48. A polypeptide according to claim 46 in which the linker comprises an antibody hinge sequence selected from the sequence given in SEQ ID NO:53, SEQ ID NO:54, SEQ ID NO:55, SEQ ID NO:56, SEQ ID NO:57, SEQ ID NO:58, SEQ ID NO:59, SEQ ID NO:60 or SEQ ID NO:61. 